The overall objective of the proposed research is to investigate the mechanisms of synaptic plasticity (i.e. modifiability) in the nucleus tractus solitarius (NTS), a brainstem region that serves as the first relay station for many cardiopulmonary afferent inputs. Previous studies using animal models in vivo revealed various memory-like behaviors in respiratory control. The recent discovery of several forms of synaptic plasticity in NTS neurons in vitro provided a possible cellular correlate for such respiratory memory. With the use of an in vitro brainstem slice preparation and whole cell recording and field potential recording techniques for studying synaptic transmission in primary afferent pathways, the present project seeks to discern and characterize the family of synaptic plasticity expressed in the NTS and to elucidate the corresponding cellular mechanisms of their expression. Of particular interest are the conditions for the induction of various forms of long- term, short-term and phasic plasticity as well as the possible cellular mechanisms underlying their expression, including various excitatory and inhibitory amino acid receptors, serotonin receptors and intracellular calcium signaling. Five specific aims are proposed to investigate these mechanisms. The results obtained will provide valuable insights into the mechanisms of afferent signal integration in the NTS and the corresponding effects on respiratory control.